Madcow Super DX3 Build Thread

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Dave,

Very nice build thread... the Super DX3 is a great kit. You'll really enjoy how well it fly's.

Looking forward to your updates,
Spicer
 
Green Jello said:
Hey, thanks. That really described what I was seeing. I guess it's possible I just wasn't stirring enough.
Click to expand...

No problem. I just found it and did one set on my Mini Eagle Claw. I found the "mayonnaise consistency" as suggested much easier to work with.
 
Fill Tube Spirals and Fin Fillets:

Parts Involved:
- Fin Can Body Tube Section (Kit)
- Upper Body Tube

Other Supplies:
- Bondo Glazing and Spot Putty
- Medium Grit Sandpaper
- Fine Grit Sandpaper


Summary: This is always the most tedious step in any cardboard tube rocket build. I filled the tube spirals and fin fillets and and sanded the entire rocket smooth.


Step 1 - Fill Tube Spirals: I took Bongo Glazing and Spot Putty and filled the tube spiral gap on both body tubes with the tip of my finger. The lower tube needed it in both lines, where the upper tube really only needed the main one. Let dry at least an hour or so.
IMG_4094.jpgIMG_4100.jpg


Step 2 - Sand Fillets and Fill With BGSP: Next I took some 150 grit sandpaper and smoothed out the fin fillets as best I could. Epoxy with phenolic microballoons sands pretty easy, so you need to be careful not to remove too much material. Once I had them the shape I wanted, I ran a coat of Bondo Glazing and Spot Putty all over each fillet. This fills any holes and imperfections.
IMG_4103.jpg


Step 3 - Sand Entire Rocket Smooth: Once all the BGSP is completely dry, you can begin the endless process of sanding it all off. I use 220 grit sandpaper for this task. You have to be careful with the tube spirals to stop at the perfect time when the excess is gone and it just fills the gap.

​
 
Looking Good Dave! Man do I know what thats like having just finished all the sanding on the Patriot! And I believe the DX3 is a bit taller!
 
Anyone have any input on a good starting point for how much BP to use in ejection charges on a 4" rocket of this size?
 
dgreger said:
GJ, here's a link I found that I will probably use.
https://www.info-central.org/?article=303
Click to expand...

That's the spreadsheet I used for my paper Super DX3. With three 2-56 nylon sheer pins on both booster and NC I ended up at 1.2g of 4Fg for both after calculation with 2x margin for ejection force and +33% margin for BP mass. Worked perfectly in ground test and 3 flights including two DD. On last DD, I had 1.3g in apogee charge ( too lazy to remeasure... more is better etc.) and noticed some cracking in paint on body tube near ejection well. Tells me that 1.3g is getting pretty close to "blow it up" for this rocket.
 
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I started with some ejection charge testing today. I did 2 tests with 1.2g and they both looked like this:

[video=youtube_share;536J6B2GZTE]https://youtu.be/536J6B2GZTE[/video]

Do you guys think that's powerful enough, or should I go to 1.5g?
 
Green Jello said:
I started with some ejection charge testing today. I did 2 tests with 1.2g and they both looked like this:

[video=youtube_share;536J6B2GZTE]https://youtu.be/536J6B2GZTE[/video]

Do you guys think that's powerful enough, or should I go to 1.5g?
Click to expand...

That does look a little weak. The ground test below was definitely more energetic using 1.2g Goex FFFFg (measured on a 0.1 g scale), Quest Q2G2 igniter and 3x 2-56 nylon sheer pins with brass shims on the NC. You can see the shock cord is straight out even with the main starting to deploy and still some decent recoil. The ejection charge is in a PVC well mounted back on the bulkhead in this case, so perhaps that makes a difference.
View attachment 141539View attachment 141540View attachment 141541View attachment 141542
Really enjoy your posts BTW. My current main project is a Wildman Jr. that will eventually be two stage, so it looks like we are swapping kits!
 
WoShuGui said:
That does look a little weak. The ground test below was definitely more energetic using 1.2g Goex FFFFg (measured on a 0.1 g scale), Quest Q2G2 igniter and 3x 2-56 nylon sheer pins with brass shims on the NC. You can see the shock cord is straight out even with the main starting to deploy and still some decent recoil. The ejection charge is in a PVC well mounted back on the bulkhead in this case, so perhaps that makes a difference.
Really enjoy your posts BTW. My current main project is a Wildman Jr. that will eventually be two stage, so it looks like we are swapping kits!
Click to expand...

Hmm....these 1.2g charges are also in a PVC well. I did use dog barf in there. Do you think that could be the difference? Good luck on your Wildman Jr.!
 
Green Jello said:
Hmm....these 1.2g charges are also in a PVC well. I did use dog barf in there. Do you think that could be the difference? Good luck on your Wildman Jr.!
Click to expand...
Dog barf, that's interesting. Wonder if it is compressible enough to absorb a noticeable amount of the ejection energy? Below is a picture of the forward bulkhead with charge PVC wells used in the ground test. A little different than yours since the charge canister is a PVC cup covered with masking tape (one of them is shown out of the well). Doesn't seem like that would explain the difference though.
View attachment 141574
 
You can't compare like that, both rockets don’t seems to have the same length at all, so the volume is probably different, aside you have a parachute so it even reduce the volume more. It’s the gas create by the explosion of the BP that eject the nose, so different volume = different pressure.
 
Area66 said:
You can't compare like that, both rockets don’t seems to have the same length at all, so the volume is probably different, aside you have a parachute so it even reduce the volume more. It’s the gas create by the explosion of the BP that eject the nose, so different volume = different pressure.
Click to expand...

WoShuGui would have to confirm, but I'm pretty sure that's the EXACT same kit.
 
Area66 said:
You can't compare like that, both rockets don’t seems to have the same length at all, so the volume is probably different, aside you have a parachute so it even reduce the volume more. It’s the gas create by the explosion of the BP that eject the nose, so different volume = different pressure.
Click to expand...

Not sure the volumes are that different. They are both Madcow 4" paper Super DX3 kits. Mine has a 17" payload tube minus 3.75" for AV bay minus NC coupling (call that ~ 3.5" 'cus it is rounded).
 
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Hey all... I did a bunch of work on this thing this past weekend and didn't really take a ton of pics. So I'm going to just abandon the format of my build steps (not sure if anyone cares) and just post some pics.

IMG_4104.jpgIMG_4105.jpgIMG_4106.jpgIMG_4107.jpg

The thing is fully primed and sanded with 3 coats. All the holes for venting, shear pins, plastic rivets and rail buttons are drilled. Right now I'm building a temporary paint booth and I'll be appyling the paint soon.
 
Green Jello said:
Hey all... I did a bunch of work on this thing this past weekend and didn't really take a ton of pics. So I'm going to just abandon the format of my build steps (not sure if anyone cares) and just post some pics.

I have enjoyed your thread build format. I can appreciate how much time you took in making detailed pictures as well as descriptions. I have only done a couple of build threads but to be detailed takes a lot of time and effort. At times it almost seems like the thread slows everything down. My last couple of builds I have taken a break from posting threads. I am looking at starting one soon. Keep up the great work and if you decide to detail another build, I'll be reading.
Click to expand...
 
I have had the same feelings regarding my build threads, and they aren't nearly as good as yours. I follow all your builds, and most of the other threads that have HPR builds. One thing I learned is that just because there are few responses, it doesn't mean people aren't interested. This thread has over 1200 views, at least 15 of them are mine.
Keep up the good work, some of the ideas and methods you post are part of my builds too!
 
Built the shock cords today. First time I've used shrink wrapping on them. I like they way they came out.

IMG_4108.JPG
 
I agree with what Wayco said above, your build threads get tons of views, its also nice to read a build thread without alot of posts going slightly off topic.
Cant wait to see it finished!
 
Green Jello said:
There is an error or change in the Super DX3 kit. The manual shows that there is only 2 CRs included, but it actually came with 3. I assume this is the way all the kits are now so you can sandwich the fin roots in between them.o epoxy fillets later.
Click to expand...

You have got to be kidding me...I just assembled my MMT and thought it looked sparse due to the length, without a 3rd CR. I even read the instructions a few times just to see if I was missing something...I need to follow my instincts better! Now it's too late for me on this HW because I would have to cut the CRs off! Not only that but I also JB Welded my engine retainer...I think I will be emailing Madcow tomorrow.
 

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